Process for utilizing coke oven gas and waste pickle liquor for the production of ammonium sulfate



June 13,

Filed May 28, 1946 June 13, 1950 w. TIDDY 2,511,306

PROCESS FOR UTILIZING COKE OVEN GAS AND WASTE PICKLE LIQUOR FOR THEPRODUCTION OF AMMONIUM SULFATE Filed May 28, 1946 2 Sheets-Shea?I 2Patented `lune 13, 1950 UNITED STATES `,PATENT OFFICE 2,511,306 rnoonssFon ufrmzino cogne OVEN' GAS AND Wasn; Home LIQUOR ron 'r1-1E PRODUCTIONor Armonium sULFa'rE William Tiddy, Manhasset, N, Y., assignor to AlliedChemical & Dye Corporation, a corporation of New York Application May.2.8, 1946,.Se1.ialNp 672,895

(Gi. 23F119) 12 Claims. l

rlhis .invention relates to the utilization of coke oven gas and .Wastepickle liquor for the production of ammonium sulfate and moreparticularly to the production .of ammonium sulfate, the re- .moval ofammonia and other constituents from coke oven gas and the .removal of.iron values from pickle liquor. .Application Ser. No. 672,896, filedMay 28, 1946, is .copending and pertains to .similar subject matter.

In .themanufacturng .and processing of steel, a Vserious Waste problem.exists in disposing of the pickle liquor produced in the cleaningofsteel with sulfuric acid. I Ihe annual production of waste pickleliquor vamounts to vabout 800,000,000 gallons. Even if it Cannot beutilized in the Vproductionof useful products, thepickle liquor,containing I as ,it doesfree sulfuric acid, presents a .seriousproblemof disposal. In fact, many coin- .munities .prohibit the disposal ofthis liquorin v streams orrivers unless it has been previouslyneutralized. .At the present time agreat .portion of .the pickle'liquor.is normally neutralized with lime .before itflovzs into streams orrivers.

frequently, steelmanufacturing plants arelocated in .closeproggimitytocoke ovens. The coke oven sas contains .ammonia and While pickle liquorisavailalnle at the steelplants, it has not ,heretofore Lprovedpracticable to utilize A.such liquor commercially ,for recovery ofammonia from vthe coke rovengas. Steelmanufacturers customarilyesort `toyuse of purchased sulfuric .acid for recovery .of ammonia from the gas.While use of relatively pure sulfuric acid iseffec- .tive for ammoniarecovery, it is relatively ex- .,pensive and `does net solve'the problemof rd is- .posal ofA pickle' liquor.

pickle liquor. Thisprocess may be vcontinuous even if .thearnountofpickle liquor varies from time to time. ABy the v utilization of Vthepikle `liquor-for the .production of useful compounds,

the .problem of .disposal of the pickle liquor is solved and materialeconomies are effected.

An object .of this .invention is .to provide a vvcontinuous. processofutilizing pickle vliquorffor .the recovery of ammonia fromunpuriiiedcoke oven gas, regardless of the relative jquantities of pickle liquorand coke Oven gas available for use in the process.

Another,.ol oject of this inventien is to utilize pickle liquor handcoke oven gas forvthe production Aof ammonium sulfateby a processWhichis "jfllerfiible in` operation and Which'isnot limited by therelative available quantities of unpuriled coke oven gas and pickleliquor.

yn the process of this invention, unpuried coke oven gas vis initiallycontacted intimately with a feed Vliquor comprising pickle liquorcontaining free sulfuric acid and ferrous sulfate and a-liquorcontaining ammonium sulfate and subsequently contacted intimately withan aqueous solution of sulfuric acid. If the amount of pickle liquoravailable from time to time varies and 4is insufficient to neutralizethe ammonia in the unpuried Vcoke oven gas, a portion of the unpurifiedcoke oven gas is contacted initially with nthe feedliquor andsubsequently With the aqueous solution of sulfuric acid.` The remainingportion of the coke oven gas is contacted solely with the aqueoussolution of sulfuric acid. The relative proportions of the volume of thecoke oven gas contacted with both the feed liquor and the aqueoussolution of sulfuric acid and of the volume contacted solely with theaqueous solu- `tionlof sulfuric acid is regulated depending upon Ythev.relative amounts of available pickle liquor and unpuriied coke ovengas.

4between the unpuried coke oven gas and the Jfeed liquor, .solubleammonium sulfate and insolubleY ferrous hydroxide, ferrous sulde andamlmonium ferroferrocyanide (NH4Fe"Fe"(CN)6) are iformed. The insolubleferrous hydroxide,

ferrous sulfide and ammonium ferroferrocyanide areseparated from theliquor by any suitable means, such as-iiltration, decantationorcentrifugation. After separation of the .insoluble materials, a portionof the liquor is recycled with additional.. pickle liquor to contact theunpurifled coke oven gas. Desirably, from to 190%, and preferablyvfrom-'Z0 to 80%, ofthe liquor isrecycled `toiformY the feed. liquor inthe process. 'Theremainingportion of the separated liquor is oxidized byaeration, fory example, to remove any residualferrous .sulfate in thatportion .of the clear liquor. The free ammonia content of this For thispurliquor-is adjusted, if necessary, by addition of ammonia-:totheliquor prior to. oxidation; thus asiioc the free ammonia content of theliquor should be at least 0.5 gram per liter, and when the ferroussulfate content of the liquor is 2 to 4 grams per liter, the freeammonia content of the liquor should be about 0.8 gram per liter orhigher. The resulting iron hydrate (Fe2O3.XH2O formed in the oxidationstep is removed by any suitable means, such as decantation, filtrationor centrifugation, and the ammonium sulfate, after such separation, isrecovered from the clear liquor by any conventional means.

The ferrous sulfate content of the feed liquor after contact with thecoke oven gas may fluctuate from D to grams per liter; the contact ofthe coke oven gas with the feed liquor is regulated so that the liquorafter contact contains not more than 10 grams of ferrous sulfate perliter and is preferably regulated so that the ferrous sulfate content ofthe liquor after contact with the gas is ordinarily within the range of2 to 4 grams per liter. A concentration of at least 2 grams per liter offerrous sulfate insures substantially that the insoluble ammoniumferroferrocyanide formed is not converted to soluble ammoniumferrocyanide. When the ferrous sulfate content of the liquor aftercontact with the gas is substantially 0 gram per liter, the free ammoniacontent of the liquor should not exceed 1.5 grams per liter in order toavoid formation of soluble ammonium ferrocyanide. The amount of ammoniumsulfate in the feed liquor prior to contact with the gas is at least 100grams per liter and is preferably at least 200 grams per liter. Theammonium sulfate content of the liquor increases during Contact with thegas, the increase ordinarily being 35 to 40 grams per liter. Withinlimits, the concentration of the ammonium sulfate in the solution aftercontact with the unpurified coke oven gas may be controlled byregulating the proportion of recycled liquor to the pickle liquorforming the feed liquor. With a pickle liquor of known concentration offerrous sulfate and sulfuric acid, this proportion can readily bedetermined.

The residual ammonia contained in the coke oven gas after contact withthe feed liquor is rremoved by contact with an aqueous solution ofsulfuric acid to form ammonium sulfate. The portion of the gas which isto be contacted solely with the aqueous solution of sulfuric acid mayconveniently be intermixed with the coke oven gas which has beencontacted with the feed liquor and the intermixed gas contacted with theaqueous solution of sulfuric acid. The ammonium sulfate formed in theaqueous solution of sulfuric acid may be recovered therefrom by anyconventional means.

Desirably, in the practice of this invention, a portion of theunpuriiied coke oven gas is contacted with the feed liquor in a chamberand the gas, after contact with the feed liquor, is subsequentlycontacted with the aqueous solution of sulfuric acid. The remainingportion of the unpurified coke oven gas which is to be contacted solelywith the aqueous solution of sulfuric acid may be intermixed with thegas after contact with the feed liquor and the resulting mixture isintroduced into the chamber containing the aqueous solution of sulfuricacid. The relative proportion of the unpuried coke oven gas which iscontacted with both the feed liquor and the aqueous solution of sulfuricacid and that which is contacted solely with the aqueous solution ofsulfuric acid is regulated so that the iron values are materiallyreduced in the feed liquor and the ammonia in the coke oven gas issubstantially completely removed. When no pickle liquor is available,all of the coke oven gas may be contacted solely with an aqueoussolution of sulfuric acid so that operation of the process of theinvention is independent of the amount of pickle liquor available.

A more comprehensive understanding of this invention is obtained byreference to the accompanying drawing, -in which:

Fig. l is a diagrammatic View showing one form of apparatus for carryingout this invention, and

Fig. 2 is a diagrammatic view showing another form of apparatus for thepractice of this invention.

In Fig. 1 pickle liquor (which ordinarily contains from 2 to 8% of freesulfuric acid and from l0 to 22% of ferrous sulfate, but which maycontain more or less of these components) is colleeted in a suitabletank Il! and is pumped through pump II, through conduit I2, to a feedtank I3. As described in detail later, the pickle liquor may beintermixed in the feed tank i3 with partially neutralized pickle liquorfrom an ammonia recovery tank i4 and recycled liquor obtained aftercontact with unpurifled coke oven gas. From the feed tank i3 the feedliquor which comprises the recycled liquor and fresh pickle liquor andmay comprise partially neutralized pickle liquor is pumped by a pump I5through conduits I6 and l1, to a reactor I8. The reactor i8, as well asthe absorber 35, the function of which will be later described, may beany suitable equipment for effecting intimate, preferablycountercurrent, contact between the coke oven gas and the feed liquor.Thus, for example, these elements may be substantially empty shellsequipped at the top with a distributor for liquor and at the base with adistributor for the gas, or either or both may be towers packed with anysuitable packing, e. g. refractory tile. From the reactor I8 the feedliquor is pumped through a conduit I9 by a pump 29 through conduits 2|and 22 to a decanter 23 which operates in a conventional manner toseparate supernatant liquor from precipitated material. The clarifiedliquor flows through conduit 62 into filtrate tank 25. It will beobserved that conduit I1 communicates with conduit 2l; this arrangementpermits feed liquor to be repeatedly recycled by pump 20 throughconduits I1 and 2l and the reactor to maintain the necessary rate offlow of liquor through the reactor to effect the desired intimatecontact between the gas and liquor. Liquor is fed from the reactorthrough conduit 22 to decanter 23 at substantially the rate at which theliquor is fed through conduit I6 to the reactor. If desired, a filter 24into which liquor from conduit 6I enters may also be provided foreffecting a more complete separation of the liquor from the precipitatedmaterial. The clear liquor is stored in a filtrate tank 25. From thefiltrate tank the clear liquor is pumped by a pump 26 through a conduit21. A portion, for example about of the total volume of the liquorpassing through the conduit 21, is recycled through the reactor througha conduit 28, the outlet of the conduit 28 being directed into the feedtank i3. The remaining portion, for example about 20%, of the totalvolume of the liquor passing through the conduit 21 is passed through aconduit 29 to an oxidizer 30.

In the practice of the process in the apparatus illustrated in thedrawing, the unpuried coke oven gas passes through a conventional f-Lottrell precipitator and -reheater vapparatus Aill and 3 I prior toentering conduits 33 and 34. Re- /heater 31" may `be utilized to reheatthe .gas to temperatures conventionally employed in :recovery of ammoniafrom coke ovenfgas. If desired, addition of hea-t to the system may zbeaccomplished -by heating `the -feed liquor Vsolution :before enteringthe reactor to a temperature such that the temperature ofthe coke-ovengas llearn ing the reactor is maintained at or above the temperature ofthe gas entering the reactor `instead of by adding heat Vto the gas bymeans of reheater 3 I Afportion ofthe )gaspassesthrough a valve 32 andconduit 33 tofreactor I8. *The remaining portion of the unpuried-gaspasses through conduits 34 and 31Ivsto an absorber35- As explainedin detail later, the vremaining portion ofl the gas together with tthergas contacted `with the feed liquor is intimately contacted with vanaqueous solution of sulfuric acid `in the yalzisorber 35. The relativelproportion of the unpurifled coke oven gas contacted with Lthe feedliquor 'in the reactorY I8 and that contacted .solely `with the aqueoussolution of sulfuric acid is regulated by the valves 32 and 36, and thisproportion is changed from time to time, depending upon the amount ofpickle liquor available with respect to the volume of 4unpuri-fled cokeoven gas to be processed. The -outlet of the conduit t3 inthe reactor IBis located desirably near the bottom thereof tov insure -thecounterourrent relationship between vthe colse oven gas Aand the feedliquor. The coltre oven `gas flows upwardly through the ,reactor ,I'8through conduit 31, in which it is intermixed ywith the -unpuriiied4coke oven gas from the 4conduit 3 4 for introduction into the absorber"35.

As heretofore described, a portion of'itl'lesliquor from the conduit2l',v for example -aboutfzot 4of the total 4volume of liquor passingAthrough the onduitl, is directed 'through aconduit vzii-to an oxidizeret. vPrior to the Yintroduction of the liquor. 'into the oxidizoreil.the ammonio Content thereof "is, raised to Preferably within #the rangev,of from j?` to 1,.'5 gramsper lifter of-free ammonia. This ammonia maybe introduced Vintofthe` liquor through a pipe 61. The ammonia -or thisvYpurpose is substantially free from cyanidesand may be obtained from anysuitable source such Aasa fixed ammonia still. iThe liquorin thetankvB-D is oxidized by means of air V-provided through apipe 33, Thesolution in the oxidizel is .blown with sufcient air, eithercontinuously or intermittently, to remove substantially completely anyferrous sulfate remaining in the liquor and r'to convert the iron valuescontained v thereinfto -insoluble ferrie hydrate. 4After treatment inthe oponer.. the vliquor containing tho ,eroioioted ferrie hydrate ispassed through a conduit -39 to ,a decanter @e or filter to remove theferrichydrate therefrom. The de canted liquor is then collected in asuitahlev collecting tank` lll,y from which it may @be `removed by moansof a pomp e2 to a conduit v43 connected to any suitable apparatus forthe recovery of ammonium sulfate in crystalline form. For example,4 thisdecanted liquor containingy ammonium sulfate may be mixed .with liquorfrom feed tgank'lll and;intro duced into absorber 3,5 and the ammoniumsulfate content ofl the liquor recovered, as hereinafter described, incrystellizer 54x To remove the small amount vof ammonia evolved from the,oxidizen the air after passage vthrough the oxidizer is brought incontact through a conduit or pipe'lwith pickle liquor i6 :in an,anunonia ,recovery i4., the. pickle liquory v'heine supplied .to .thevessel I4 from the .conduit Vl2 through a conduit 6.3. After the pickleliquor has contacted the air containing the ammonia in the ammoniarecovery tank I4, it is pumped by means of a pump 4 4 through a conduitto the feed tank I3.

The precipitated product obtained from the filter 24 orrthe decanter 23and which contains primarily iron hydrate and iron sulfide may, ifdesired, be converted substantially completely to iron oxide. From thedecanter `or filter the precipitate may be pumped to a continuous vacuumlter in which lit is washed free from ammonium sulfate and subsequentlydelivered to a drier or heat treating oven 46. In the o ven the ltercake may be heated in the presence of air. Ihe resulting precipitatecontains from 45 to 69% of iron depending upon the amount of iron hydroxide or iron oxide present. The presence of iron sulfide in theprecipitate materially assists in reducing the heat required to ydry orheat Ytreat the precipitato ffhe gasafter contacting thefeed'liquor inthe reactor, passes through the conduit 31, in which it is mixed withthe lportion of the unpuried coke oven gas passing Vthrough the Valve 36and the conduit 3.4and which .by-passed .the reactor I8. 1n the absorber35 the gas contacts intimately an aqueoussolution of sulfuric acid whichflows in countercurrent relation to the gas to remove substantiallycompletely, if desired, the residual .ammonia in the gas. To insure thisintimate contact, the Aoutlet of the conduitBI is located desirably nearthe bottom of the absorber 35. The gas flows upwardly through the ab-.sorher and passes .through ,an outlet e8. The

conduit 3,1 may be provided with a preheater (not shown) to raise thetemperature of the gas prior to introduction into theabsorber 3.5.

The aqueous solution of sulfuric acid containing ammonium sulfate forcontact with the gas inftheabsorgber 35 is pumped from a feed tank `vli]lbya pumpg through a conduit-49. The solution inthe feed tankA 41 Yissupplied with sulfuric .acid through oohout k50, with water thro-oehconduit 5I `and lrecycled liquor through oondiliil?,

The solution., after passage. through the absorberoa, flows through .aconduit. 53H00 a oryss tallizing unit 54. IThe crystallizing unit issimilar to` that .described in United States Patent No. 2,3'8.;9,01,grantedon-Februa-ry 6, 1945, to Somet- Solvay Engineering Corporation,as assignee .of yW. Tiddy. `The solution passing to the crystallizer-.54 .is...discharged adjacent to the inlet 55 of a pump.56=and ispumpedthrough the V conduit `51'I to an evaporative cooling chamber v58. Bymeans of a barometric condenser (not shown) lthe evaporative coolingchamber 58 is maintained under relatively low pressure, and the solutioncontained-l in .the evaporative cooling chamber 58 is cooled andconcentrated by evaporation of watersuiciently to ysupersaturate thesolution of ammonium sulfate. The supersat- -urated .solution passesvthrough the conduit 59 -to the bottom of -the-crystallizer `54. Thesupersaturated solution of ammonium sulfate passes upwardly-incrystallizer 54 Aover a suspension of lsolution containing'from 44713046%-l off ammonium the gas in the reactor I8. 'the feed liquor is socontrolled that the amount of sulfate radicals in the feed liquor isapproximately equivalent to the desired amount of sulfate radicals inthe recycled liquor and the feed liquor -is ordinarily so controlledthat it contains sulfate "radicals equivalent to more than 100,preferably more than 200, grams of ammonium sulfate per vliter ofrecycled liquor. flow of feed liquor and the unpurified coke oven .gasto the reactor I3 is such that from 75 to 95% 'sulfate and substantiallyfree from crystalline ammonium sulfate passes from the crystallizer 54through the conduit 52 to be recycled through the absorber with sulfuricacid and water. Desirably, suiiicient sulfuric acid and water are addedto the feed tank through conduits 50 and 5I respectively to insure aconcentration of ammonium sulfate between 40 to 45% =by weight and asulfuric acid concentration within the range of to 50 grams per liter.The solution which is supplied to the absorber 35 should preferably befrom 35 to 65 C.

In the apparatus shown in Fig. 1, a portion of the coke oven gas passesfrom the Cottrell unit 3i, through the conduit 33 to the reactor I8. Inthe reactor i8, it is contacted with feed liquor comprising pickleliquor containing' ferrous sulfate and free sulfuric acid and a recycledliquor containing ammonium sulfate. The feed liquor which is a mixtureof recycled liquor and pickle liquor and which may contain a maximum of100 grams of ferrous sulfate and 50 grams, and desirably not more than25 grams, of sulfuric acid per liter, and preferably contains at leastgrams of ferrous sulfate and at least .2 gram of sulfuric acid perliter, passes in countercurrent relation with thel gas, and intimatelycontacts The composition of Desirably, the rate of iof the iron valuescontained in the feed liquor are yconverted to insoluble compounds. Thiscan be achieved by regulating the volume of unpuriiied coke oven gaseswhich are diverted to the reactor I8 by adjustment of the valve 32. Inthe reactor, the ammonia, hydrogen sulfide and cyanogen compoundspresent in the coke oven gas react with the ferrous sulfate and sulfuricacid in the feed liquor to produce insoluble iron sulfide and hydrate,insoluble cyanide compounds, and soluble ammonium sulfate. The contacttime of the feed liquor with the gas in the reactor I8 is controlled sothat the solution withdrawn from the reactor I8 through the conduit I9has no soluble ammonium ferrocyanides and from 0 to 10, and

preferably from 3 to 4 grams, of ferrous sulfate per liter.

The solution leaving the reactor at normal gas temperatures is pumped bymeans of a pump 20 to a decanter 23, and the solution may, if desired,be filtered through the filter 24 to assure substantially completeremoval of the precipitated iron compounds. The supernatant liquid fromthe filtration is stored in a filtrate tankv 25 and is recycled andblended with raw pickle liquor in the feed tank i3 to produce a feedliquor of such concentration that (1) the resulting feed liquor containsat least 100 grams of ammonium sulfate per liter and preferably at least200 grams of ammonium sulfate per liter, and (2) the volume andconsistency of the precipitated iron hydrate and iron sulfide iscontrolled so that no blocking or high pressure differential exists inthe reactor I8.

The liquid withdrawn from the tank 25 which is not recycled and whichordinarily comprises a minor portion, for example about 20% of theliquor, is subjected to oxidation conditions to convert the remainingferrous sulfate to in- Isoluble iron hydrate by passage through theoxidizer 30. The ammonia content of the solution leaving the reactor I8desirably varies from 0.1 to 1.0 gram per liter. I f necessary,therefore, prior to passage through the oXidiZe-r 30, the ammoniacontent of the supernatant liquid is increased to contain at least 0.5gram per liter of free ammonia. The primary purpose of the oxidizer isto eliminate the remaining ferrous sulfate in the solution leaving thereactor i8 so that ammonium sulfate substantially free from iron can beobtained in the crystallization step. The reaction which takes place isamong free ammonia, oxygen and ferrous sulfate at atmospherictemperatures. The ferrous sulfate is oxidized and the ammoniaprecipitates as ferrie hydroxide, while the sulfate radical is convertedto ammonium sulfate. Substantially complete removal of the ferroussulfate is effected when the ammonia in the feed liquor contains or isstrengthened to 0.8 gram per liter and the original solution fed to theoxidizer contains from 3 to 4 grams per liter of ferrous sulfate. Thesolution in the oXidiZer is blown with air, after which substantially noferrous sulfate exists in the solution and all of the iron has beenconverted to insoluble iron hydrate. The liquor containing theprecipitated iron hydrate is transferred to a decanter 40 and the ironhydrate removed from the liquor. The clear` liquor is then collected ina tank 4i from which the ammonium sulfate may be recovered by any wellknown means. If desired, a filter may be installed between the oxidizer30 and the decanter 40 or between the decanter 4E! and collector tank 4|to remove any suspended iron hydrate carried in the supernatant liquor.

To recover the small amount of unused ammonia from the oxidizer 30, theair released from the oxidizer is contacted with fresh pickle liquor inthe ammonia recovery tank i4, and the free sulfuric acid in the pickleliquor readily absorbs this ammonia. The pickle liquor, after absorptionof the ammonia, passes to the feed tank i3.

The oxidation step may be omitted, if the presence of a small amount ofiron in the ammonium sulfate recovered by the method is notobjectionable. In that procedure, the separated liquor passing throughthe pipe 29 is directly processed to recover the ammonium sulfate fromit by any conventional means, such as evaporation. However,substantially iron-free ammonium sulfate is ordinarily required, and themethod desirably includes' the oxidation step.

The remaining portion of the unpuriiied coke oven gas from the Cottrellunit 3l which is not diverted through the reactor i8, passes through theabsorber 35 and is intimately contacted therein with an aqueous solutionof sulfuric acid which also contains ammonium sulfate. In the absorber,the residual ammonia contained in the coke oven gas is removedSubstantially completely. The ammonium sulfate which is formed isrecovered in the crystallizer 54. When a large amount of pickle liquoris available, all or the greater portion of the unpurii'ied coke ovengas can be circulated through the reactor I8. However, when there issubstantially little pickle liquor available, only a portion of the cokeoven gas would be circulated through the reactor I8.

. In fact, at times if there is no pickle liquor avail- 9 The rates offlow ofV the coke oven gas and pickle liquor together with other dataofatypical run in the reactor shown in Figs. 1 and 2j are as follows:

Gas rate of coke oven gas-cu. ft. per

hour 10,000

NH3 content of gas-lb. per 10,000 cu. it. 6 Pickle liquory used:

Composition FeSo4, per cent 16.7 H2504, per cent 8.5 Volume per hour,per cent of feed to reactor 23.5

(Remaining 75l-,80% is recycled liquor.) Feed to reactor.:

Composition:

FeSOi, g. p. l 49.0 H2504, g. p. 1 25.0 Rate, gallons per hour 33.1 Feedt thickener or decanter, gal. per

hour 33.1 Volume of ltrate plus clariiied liquor from decanter orthickener plus Water washing of cake, gal. per hour 35.6 Volume returnedto system for blending with fresh pickle liquor, gal. per hour 25.3Volume to oxidizer, gal. per hour 10.3 Volume to collector tank forammonium sulfate recovery unit, gal. per hour 10.3 Composition, g. p. 1,(NH4)2SO4 300 Filter cake produced from filtration of thickened slurryfrom decanter, pounds- 29.9 Composition of Wet washed cake (dry basis):

FeS, per cent 89 Insoluble ammonium` ferroferrocyanide, per cent '7 Ironhydrate, per cent 4 Moisture content or filter cake, per cent 65 Weightof cake dried at 105 G., pounds 8.6 Ammonia recovery, percent 90 InFig.l 2 there is illustrated a modification of the apparatus shown inEig. 1. Instead of the scrubber operation in conjunction with acrystallizer for contacting thev vglas with the aqueous solution ofsulfuric acidand the recovery of amonium sulfate, the system shown inFig. 2 includes a standard ammonium sulfate saturator. The apparatusemployed for contacting the gas with the blended feed liquor includingthe pickle liquor, however, is identical with that shown in Fig. 1.

In Fig.` 2, pickle liquor is collected in a suitable tank l!!! an@ ispumped through @conduit l|2ebvapum Hr! te.: iced task H3- Fromme feedtamis |13 feed. lunar comarising recycled 11140.17 and. fresh. Ei'lle$1909? is Pumped by pump ||5 through conduits7 l@ and H1 to a reactor I0. Frein the. rcactcr. .L8 the feed liquor is planned through. @adults'la aad l?? to. a gesamter |23.- A. .lter |24 .icio which ist@ liquorfrom @enduit |6| enters may alsovbe employed to effect a incre @ongletsSeparates Qf the .lisser from the preaiutate@ material, The @Isar llegaris .Si/cred in la filtrate taak |25 Prem the ltrate taak the. clearliquor is'rlipsd. by pump. |25 through a conduit |721." A prtion'of thetotal volume Qi liquor passing through conduit |21 is recycled throughconduit |'.f 8 to the feed tank l |31Y yThe remaining portion of theclear liquor passes through a conduit |29Y to an oxidizer |30.

A portion of the unpuried coke oven gas passes from the CottrellVprecipitator Vand "11e- 10 heater unit 3|, w3| to the reactor 8 throughthe conduit |33 and lows'therein in countrcvr! rent relation with theflow of the feedliquor. The remaining portion of the unpuried 'coke ovengas passes throughconduits la@ and |31y to a saturator |750. A preheater(not shown) may be provided in the conduit i3?, to insurathat thetemperature of the gas introduced into the saturator is sufficientlyhigh to effect eyapoation of water atan adequate-`rate in thesaturator.` The portion of the coke oven gas after passage through theAreactor I8 iiows through theconduit |36 to ble intermiied in the conduit|31 with the unpuriiied coke oven gas which Joy-passed the reactor.Suitable valves are provided in the conduits |33 and |34 to regulate therelative proportion of unpulriflled coke oven -gas which passes throughthe reactory ||8 and' that which by-passes the reactor I9.

rI he ammonia content of the portion of the feed liquor which passes tothe oxidizer |30 is preferably raised to within the range of from .7 to1.5 grams per liter of free ammonia. "Ihe liquor in the tank |30oxidized by means of air provided through pipe |38. After treatment "inthe oxidizer, the liquor containing precipitated ferric hydrate ispassed through conduit V|39 Vto a decanter |40. The decanted liquor iscollectedI in a suitablev tank |d| from which it is removed as desiredby means of pump |42 through a conduit |43 connected to any suitableapparatus for the recovery of ammonium sulfate. The ammonia contained inthe air, after passage through the oxidizetr', is contacted with pickleliquor in ammonia recovery vessel Il, and the resulting liquor is pumpedthrough conduit |45 by pump |44"to be added to the liquor cori:-r tainedin feed tankv ||3.

The gas, after contact with the feed liquor in the reactor, isvintermixed with the unpuried coke oven gas which by-passes the reactorin the conduit |37 and the mixed gas is contacted with an aqueoussolution of sulfuric acid in the saturator |50. The saturator may beprovided with a gas inlet |5| in the form of a perforated ring. Aftercontact with the aqueous solution of sulfuric acid in the saturator |50,the gas passes through conduit |52 to an acid separator |53 to removeany 'entrained sulfuric acid, and thence through an outlet |54 in theacid separator |53, to the nal cooler. In the saturator |50 the residualammonia in the coke oven gas is substantially completely removed. Theammonium sulfate formed as a result oi the interaction between theammonia and suliuric acid in the saturator may be conveniently recoveredby passing the crystals of ammonium sulfate with the supersaturatedsolution thereof through the conduit |55 to a drain table |56 andconveying the resulting crystals through a conveyor |51 to a centrifugaldrier |58.

One important difference in the reaction occurring in the saturatorshown in Fig. 2 from the scrubber-crystallizer system illustrated inFig. 1 is that an increase from 5 to 10 C. in the temperature of the gasintroduced into the saturator or preheating the solution before entenngthe saturator is necessary to make up the deficiency of heat requiredfor the evaporation oi water introduced into the saturatorl This heatloss is due'primarily to the lower ammonia content of the gas Venteringthe saturator, which reduces the amount of heat developed in thereaction between ammonia and sulfuric acid.

commercial equipment there are two advantages in the practice of thisinvention involved in the utilization of the apparatus shown in Fig. lover that illustrated in Fig. 2. These advantages are: (l) easiercontrol of operation of the absorber and crystallizer than thatexperienced with the use of the saturator, and (2) there is a much lowerdifferential in the absorber shown in Fig. 1 than in the saturatorillustrated in Fig. 2. l.With typical commercial apparatus thisdifferential is 3" of water in the apparatus shown in Fig. l and 25" ofWater in the system illustrated in Fig. 2. This advantage is anappreciable one in terms of tons of ammonium sulfate produced, since100% of the gas in all cases passes through Ythe absorber or saturator,Whereas 100% of the ammonia does not pass through the saturator or theabsorber. Further, carrying out the process as hereinabove disclosed inconnection With Fig. 1 results in production of substantially uniformammonium sulfate crystals as compared with those produced by the processof Fig. 2.

It will be obvious from the above description that various changes maybe made without departing from the scope of the invention. Thus, forexample, while for the purpose of economy I prefer to blend recycledliquor containing ammonium sulfate with the pickle liquor to form thefeed liquor employed in the process, the pickle liquor may be blendedwith ammonium sulfate solution from other sources to form the feedliquor. Further, the liquor from the reactor (after separation ofprecipitate) may be continuously introduced both into the feed tank andoxidizer, or may be alternately fed to the tank and oxidizer for timeperiods such that the desired proportions of the liquor are recycled andoxidized. Blending of the pickle liquor and recycled liquor may beaccomplished in the presence of the coke oven gas, for example, byseparately spraying the liquors into the top of the reactor. Ammoniafrom any desired source, e. g. the con- Ventional ammonia still, may beutilized at any point in the process, for example, such ammonia may bemixed with the coke oven gas before it enters the reactor, or may beintroduced into the feed tank to neutralize partially the pickle liquorbefore entry of the liquor into the reactor.

As hereinabove described, contact between the coke oven gas and theliquor is preferably effected in countercurrent manner in suitabletowers. However, the gas may be intimately contacted with the liquor inother types of apparatus, for example, the gas may be passed through asaturator-type chamber containing a body of pickle liquor diluted withrecycled liquor containing ammonium sulfate while maintaining theprecipitate suspended in the liquor by agitation. Recycled liquor andpickle liquor may be added t the saturator as required and reactedliquor drawn off and filtered or decanted for oxidation and recycling tothe chambers.

In carrying out the invention, it is important that the coke oven gascontain hydrogen sulfide and ammonia, but it is not essential that otherconstituents which are capable of being removed by conventional cokeoven gas purification processes be present in the gas. Further, otherinert gases containing ammonia and hydrogen sulfide may be utilized inaccordance with the invention. The gas may be contacted with the feedliquor at temperatures ordinarily employed in conventional processes forrecovery of ammonia from coke oven gas, for example, from 35 to 70 C.

The terms and expressions which I have employed are used as terms ofdescription and not of limitation, and I have no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but recognize thatvarious modifications are possible within the scope of the inventionclaimed.

What is claimed is:

1. A cyclic process for producing ammonium sulfate comprising contactingunpurified coke oven gas with a feed liquor comprising a mixture ofpickle liquor containing ferrous sulfate and free sulfuric acid and arecycled liquor containing ammonium sulfate, thereby removing a portionof the ammonia from the gas, separating the liquor from the resultingprecipitate formed, recycling a portion of the separated liquor forblending with the pickle liquor to form said feed liquor for contactwith the unpurified coke oven gas, passing an oxygen-containing gasthrough the remainder of said separated liquor in the presence of freeammonia, whereby substantially all of the iron sulfate in said liquor isreacted to form ammonium sulfate and the iron values are converted toiron hydrate, separating the iron hydrate from the resulting ammoniumsulfate solution, and scrubbing coke oven gas which has passed out ofcontact with said feed liquor with an aqueous solution of sulfuric acidcontaining said last-named ammonium sulfate solution for removal of theremainder of the ammonia from said gas.

2. A cyclic process for producing ammonium sulfate comprising contactingunpuriied coke oven gas with a feed liquor comprising a mixture ofpickle liquor containing ferrous sulfate and free sulfuric acid and arecycled liquor containing ammonium sulfate, separating the liquor fromthe resulting precipitate formed, recycling from 60% to 90% of theseparated liquor for blending with pickle liquor to form said feedliquor` for contact With the unpurified coke oven gas and contacting thecoke oven gas with an aqueous solution of sulfuric acid whereby theresidual ammonia contained in said coke oven gas is substantiallyremoved.

3. A cyclic process for producing ammonium sulfate comprising passingunpurified coke oven gas successively through a first chamber and asecond chamber, passing a feed liquor comprising a mixture of pickleliquor containing ferrous sulfate and free sulfuric acid and recycledliquor containing ammonium sulfate through said first chamber inintimate contact with said coke oven gas, whereby the iron valuescontained in said feed liquor are materially reduced, and passing anaqueous solution of sulfuric acid through said second chamber inintimate contact with the coke oven gas whereby the residual ammonia inthe coke oven gas is substantially completely removed. I

4. A cyclic process for producing ammonium sulfate comprising passingunpuriied coke oven gas through a plurality of chambers in sequence,passing through one of said chambers a feed liquor comprising a mixtureof pickle liquor and recycled liquor containing ammonium sulfate andpassing an aqueous solution of sulfuric acid through another of saidchambers in countercurrent relation to the coke oven gas whereby theammonia in the coke oven gas initially reacts with the iron salts in thefeed liquor, and the residual ammonia in the coke oven gas, after theinitial reaction, is removed Substantially completely by reactionprimarilyn with the aqueous solution of sulfuric acid, separating theliquor from the precipitated iron compounds formed by contact of the gaswith the feed liquor and recycling a portion of the resulting` clearliquor for blending with the pickle liquor to form said feed liquor.

5. A process for the recovery of ammonia as ammonium sulfate from gascontaining ammonia and hydrogen sulfide, which comprisesv intimatelycontacting the gas with pickle liquor containing free sulfuric acid andiron sulfate, whereby the major portion of the iron in` the pickleliquor is precipitated and the ammonia in the gasreactsv with thesulfate radicals of the liquor to form ammonium sulfate, withdrawingliquor from the zone of contact, separating withdrawn liquor containingdissolved ammonium sulfate and ferrous sulfate from the precipitate,oxidizing separated liquor with air in the presence of free ammonia toform additional ammonium sulfate and intimately contacting the resultinggas with an aqueous solution of sulfuric acid substantially free of ironvalues whereby the residual ammonia contained in said gas issubstantially removed to form ammonium sulfate.

6. A cyclic process for recovering ammonia from unpuriiied coke oven gascontaining ammonia, hydrogen sulfide and cyanogen compounds and recoveryof iron values from pickle liquor containing free sulfuric acid andferrous ilfate, which comprises blending pickle liquor containing freesulfuric acid and ferrous sulfate with recycled liquor containingammonium sulfate to produce feed liquor containing from .2 to G grams offree sulfuric acid, from 20 to 100 grams of ferrous sulfate and at least100 grams of ammonium sulfate per liter of the feed liquor, passing saidunpuried coke oven gas through reactor and absorber chambers insequence, passing s id feed liquor through the reactor chamber incountercurrent relation to the coke oven gas, and an aqueous solution ofsulfuric acid through the absorber in countercurrent relation to thecoke oven gas, whereby hydrogen sulfide and cyanogen compounds and aportion of the ammonia present in the coke oven gas react with the ironsalt in the feed liquor to form ammonium sulfate and to precipitate ironhydrate, iron sulide and ammonium ferroferrocyanide and the residualammonia present in the coke oven gas is removed substantially completelyby reaction in the absorber chamber with the sulfuric acid passingtherethrough, regulating the flow of feed liquor through said reactorchamber so that the ferrous sulfate content of the liquor leaving saidreactor chamber does not exceed l0 grams per liter and the free ammoniacontent of the liquor leaving the reactor chamber falls within the rangeof .1 to 1 gram per liter, separating the precipitate from the liquorleaving the reactor chamber, recycling from 60% to 90% of the separatedliquor to the reactor chamber with pickle liquor for contact withadditional coke oven gas, passing an oxygen-containing gas through theremainder of said separated liquor in the presence of at least .5 gramper liter of free ammonia, whereby substantially all of the sulfateradical in said oxidized liquor is reacted tn form ammonium sulfate andthe iron values in the liquor are converted to iron hydrate, and

I4 separating the iron hydrate4 from the.. resultantV ammonium sulfate:solution 'l'. A: process as defined in .claim 6 in which the ferroussulfate content. of the liquor leaving the reactor chamber issubstantially maintained within. the. range. of from 21to 4' grams perliter andthe ammonium sulfate content of the liquor introduced into the.reactor chamber is at least 209'. gramsper liter.

8: A, process` for: recovery of ammonia as ammonium sulfate from gasescontainingv ammonia and hydrogen sulfide,v and recovery of iron, valuesfrom pickle liquor containing ferrous. sulfate, whichi compriseslforming a feed liquor containingh at; least, 101)' grams of ammoniumsulfate, not more than 25 grams of free sulfuric acid, and from 20 toV100 grams of ferrous sulfate per liter, by blending ammonium sulfatesolution with pickle liquory containing ferrous` sulfate, intimatelycontacting said; feed* liquor with said gas,v whereby?A iron valuesofsaifl liquor are precipitated as iron hy i1ate.andV sulde, separatingthe precipitate from the liquoizrecycling a portion of the.Y separatedliquor together with pickle liquor inito-` intimate .contact withadditional gas containing amrnonia and hydrogen sulfide, oxidizingthe-remainder of said liquor in the presence of free ammonia,VAandintirnately contacting the resulting gas with an aqueousv solution ofsulfuric acid substantially free of iron values whereby the residualammonia contained in said gas is substantially removed to form ammoniumsulfate.

9. A cyclic process for the recovery of ammonium sulfate from unpurifedcoke oven gas, which comprises dividing the unpuried coke oven gas intotwo portions, contacting one portion of said coke oven gas successivelywith a blended pickle liquor containing free sulfuric acid, ferroussulfate and recycled liquor containing ammonium sulfate, and with anaqueous solution of sulfuric acid substantially free of iron, contactingthe second portion of said coke oven gas directly with said aqueoussolution of sulfurie acid and regulating the relative proportion of theunpuried coke oven gas which is contacted with both the blended pickleliquor and the aqueous solution of sulfuric acid and that which iscontacted directly with the aqueous solution of sulfuric acid so that amaterial amount of the iron values in the blended pickle liquor isprecipitated out and the ammonia in the coke oven gas is substantiallycompletely removed.

10. A cyclic process for recovery of ammonia as ammonium sulfate fromgases containing ammonia and hydrogen sulfide, which comprisesintimately contacting the gas with feed liquor comprising a mixture ofpickle liquor containing free sulfuric acid and iron sulfate andrecycled liquor containing ammonium sulfate, whereby iron in the feedliquor is precipitated and a portion of the ammonia in the gas reactswith sulfate radicals of the liquor to form ammonium sulfate, separatingliquor containing dissolved ammonium sulfate from the precipitate,recycling a portion of the separated liquor with additional pickleliquor into Contact with additional coke oven gas, and passing said cokeoven gas after it passes out o-f contact with said feed liquor intocontact with an aqueous solution of sulfuric acid for removal of theremainder of the ammonia from said gas.

11. A cyclic process for recovery of ammoniaas ammonium sulfate fromgases containing ammonia and hydrogen sulde, which com-prises intimatelycontacting the gas with feed liquor com- 15 prising pickle liquorcontaining free sulfuric acid and recycled liquor containing ammoniumsulfate, whereby iron in the feed liquor is precipitated and a portionof ammonia in 'the gas reacts with sulfate radicals of the liquor toform ammonium sulfate, separating liquor containing dissolved ammoniumsulfate from the precipitate, recycling a portion of the separatedliquor with additional pickle liquor into contact with additional cokeoven gas, passing an oxygen-containing gas through the remainder of saidseparated liquor in the presence of free ammonia, whereby substantiallyall of the iron sulfate in said liquor is reacted to form ammoniumsulfate and the iron values are converted to iron hydrate, separatingthe iron hydrate from the resultant ammonium sulfate solution, andscrub- Icing coke oven gas which has passed out of contact with saidfeed liquor with an aqueous solution of sulfuric acid containing saidlast-named ammonium sulfate solution for removal of the remainder of theammonia from said gas.

12. Arprooess for recovery of ammonia as ammonium sulfate from gasescontaining ammonia and hydrogen sulfide and recovery of iron values frompickle liquor containing ferrous sulfate, which comprises forming a feedliquor containing at least 100 grams of ammonium sulfate, not more than25 grams of free sulfuric acid,

and from 20 to 100 grams of ferrous sulfate per liter, by blendingammonium sulfate solution with ferrous sulfate derived from pickleliquor, intimately contacting said feed liquor Withsad gas, whereby ironvalues of said liquor are precipitated as iron hydrate and iron sulde,separating the precipitate from the liquor, recycling a portion of theseparated liquor together with ferrous sulfate derived from pickleliquor into intimate contact with additional gas containing ammonia andhydrogen sulfide, oxidizing the remainder of said liquor in the presenceof free ammonia, and intimately contacting the resulting gas with anaqueous solution of sulfuric acid substantially free of iron valueswhereby the residual ammonia contained in said gas is substantiallyremoved to form ammonium sulfate.

WILLIAM TIDDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Tiddy Feb. 6, 1945 Certificate of CorrectionPatent No. 2,511,306

June 18, 1950 l WILLIAM TIDDY It is hereby certified that error appearsin the printed specification of the above numbered patent requiringcorrection as follows:

Column 5, line 58, for preciiptated read precipitated; column 9, line62, after the numeral and period 123. insert the following Sentence: Thesupernatant liquor i l then passes through conduit 162 tuto filtratetaule 125.;

and that the Said Letters Patent should'be reed as corrected above, sothat the same may conform to the record of the case in the Patent Ofce.

Signed and sealed this 14th day of November, A. D. 1950.

- l [SNL] l l THOMAS F. MURPHY, t/

Assistant Oommzssz'ouer of Patents.

1. A CYCLIC PROCESS FOR PRODUCING AMMONIUM SULFATE COMPRISINGCONTRACTING UNPURIFIED COKE OVEN GAS WITH A FEED LIQUOR COMPRISING AMIXTURE OF PICKLE LIQUOR CONTAINING FERROUS SULFATE AND FREE SULFURICACID AND A RECYCLED LIQUOR CONTAINING AMMONIUM SULFATE, THEREBY REMOVINGA PORTION OF THE AMMONIA FROM THE GAS, SEPARATING THE LIQUOR FROM THERESULTING PRECIPITATE FORMED, RECYCLING A PORTION OF THE SEPARATEDLIQUOR FOR BLENDING WITH THE PICKLE LIQUOR TO FORM SAID FEED LIQUOR FORCONTACT WITH THE UNPURIFIED COKE OVEN GAS, PASSING AN OXYGEN-CONTAININGGAS THROUGH THE REMAINDER OF SAID SEPARATED LIQUOR IN THE PRESENCE OFFREE AMMONIA, WHEREBY SUBSTANTIALLY ALL OF THE IRON SULFATE IN SAIDLIQUOR IS REACTED TO FORM AMMONIUM SULFATE AND THE IRON VALUES ARECONVERTED TO IRON HYDRATE, SEPARATING THE IRON HYDRATE FROM THERESULTING AMMONIUM SULFATE SOLUTION, AND SCRUBBING COKE OVEN GAS WHICHHAS PASSED OUT OF CONTACT WITH SAID FEED LIQUOR WITH AN AQUEOUS SOLUTIONOF SULFURIC ACID CONTAINING SAID LAST-NAMED AMMONIUM SULFATE SOLUTIONFOR REMOVAL OF THE REMAINDER OF THE AMMONIA FROM SAID GAS.